The present invention relates to a method for springing a movement of an implement of a work machine during a movement of the work machine, in which at least one hydraulic cylinder is operatively connected to the implement. In other words, the invention relates to a method for damping the vibrations of the implement during the movement of the work machine.
In particular, the invention relates to springing of the load arm. For springing of the load arm, the lifting cylinders of the work machine are controlled. Springing of the load arm is used to increase the comfort for the driver and to reduce spillage of material from the implement (the bucket). With springing of the load arm, the load arm can move in relation to the body of the machine, resulting in two movable masses instead of one.
The invention will be described below in connection with a work machine in the form of a wheel loader. This is a preferred but in no way limiting application of the invention. The invention can also be used for other types of work machines (or work vehicles), such as an excavator loader (backhoe) and excavating machine.
WO 99/16981 describes a system for springing of the load arm. An accumulator is connected to a piston side of the hydraulic cylinder. A tank for hydraulic fluid is connected to a piston-rod side of the hydraulic cylinder. The system comprises a plurality of valves for controlling the function.
It is desirable to provide a method that provides a springing of the movement of the implement during transportation and that makes energy-efficient operation possible.
According to an aspect of the present invention, a method is provided for springing a movement of an implement of a work machine during a movement of the work machine, in which at least one hydraulic cylinder is operatively connected to the implement, comprising the steps of connecting a hydraulic machine to communication with the hydraulic cylinder, and of controlling the hydraulic machine in response to a disturbance acting upon the implement during the movement. The springing method can, for example, be initiated by the operator moving a control in the cab of the vehicle.
The hydraulic cylinder is preferably adapted to move an implement in order to perform a work function. According to a first example, the hydraulic cylinder comprises a lifting cylinder for moving a load arm which is pivotably connected to a vehicle frame, the implement being arranged on the load arm. According to a second example, the hydraulic cylinder comprises a tilting cylinder for moving the implement which is pivotably connected to the load arm. According to a third example, the hydraulic cylinder is arranged to steer the vehicle when it is being driven.
The method preferably comprises the step of controlling the hydraulic machine in such a way that said springing of the movement of the implement is achieved.
According to yet another preferred embodiment, the method comprises the steps of detecting a parameter that is indicative of the position of the implement and of controlling the hydraulic machine in response to the detected position. For springing of the load arm, the position of the load arm is preferably detected. For example, the position of the piston rod is detected via a linear sensor or alternatively the angular position of the load arm can be detected via an angle sensor. The position parameter is preferably detected repeatedly, suitably essentially continuously, and the hydraulic machine is controlled in response to this.
According to yet another preferred embodiment, the method comprises the step of pressurizing the hydraulic cylinder to such an extent that the implement is brought to a home position. The hydraulic machine is preferably controlled continuously so that the implement is kept within a predetermined range around the home position.
According to yet another preferred embodiment, the method comprises the steps of detecting the position of the implement upon initiation of the method, of defining the detected position upon initiation as a home position and of controlling the hydraulic machine, when the hydraulic machine is connected to the hydraulic cylinder, in such a way that the implement is kept in the home position.
According to yet another preferred embodiment, the method comprises the step of supplying a corresponding quantity of hydraulic fluid to the hydraulic cylinder, in the event of a disturbance that results in an upward movement of the implement. At the same time, an opposite side of the hydraulic cylinder is drained. The drained hydraulic fluid can, for example, be taken back to the hydraulic machine or to the tank.
In a corresponding way, the method preferably comprises the step of draining at least a corresponding quantity of hydraulic fluid from the hydraulic cylinder, in the event of a disturbance that results in a downward movement of the implement. According to an example, a quantity of hydraulic fluid is drained that corresponds to the size of the disturbance acting upon the implement. In such a case, the implement returns directly to the home position. According to a variant, a greater quantity of hydraulic fluid is drained than the quantity that corresponds to the size of the disturbance acting upon the implement. In such a case, the implement reaches a level below the home position, before it is brought up again.
The method suitably comprises the step of connecting a first port on the hydraulic machine to a piston side of the hydraulic cylinder via a first line. In a corresponding way, the method preferably comprises the step of connecting a second port on the hydraulic machine to a piston-rod side of the hydraulic cylinder via a second line.
According to yet another preferred embodiment, the method comprises the step of allowing the hydraulic machine to be driven by a flow of hydraulic fluid from the hydraulic cylinder, in the event of a disturbance that results in a downward movement of the implement, and of regenerating the energy from the hydraulic machine via an electric machine.
Further preferred embodiments and advantages of the invention emerge from the following description.